http://www.kloonigames.com/blog/games/crayon/ Why haven't I heard of this yet? It's a little physics engine where you draw shapes and see how they effect the current environment, ultimately to lead a red ball into a star. The downloadable version is a prototype done in under a week, while the deluxe version, which will let you draw more shapes than just rectangles and effect the on things physics with stuff like hinges, is currently in development, with a demo video below.
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It's stuff like this I bought a DS for, and now people are putting it on PC instead?